The present invention relates generally to dock levelers. More particularly, the present invention relates to a dock leveler support leg system and method for reducing the effects of stump-out and free fall.
Dock levelers are mounted on loading docks and are used to bridge the gap between a loading dock and the end of a vehicle parked at the loading dock. For example, trucks or tractor trailers may be loaded and unloaded at loading docks with the help of a dock leveler. The dock leveler enables material handling equipment such as a fork lift to move between the dock and the vehicle bed. Because not all vehicle beds are of the same height, many dock levelers are configured to pivot up and down in order to adjust and create a bridge between the loading dock and the vehicle bed. Typical dock levelers include a ramp portion. In addition, dock levelers may include a lip mounted at the end of the ramp. When a vehicle backs up to the dock, often the lip is extended and rests directly on the bed of the vehicle. Some dock levelers use the bed of the vehicle as a support for the lip and the ramp so that vehicles, such as fork lifts, material, and operators move between the vehicle bed and the dock.
If a vehicle, whose bed is supporting the dock leveler, were to pull away from the dock, the dock leveler may become unsupported and move rapidly down to a low position under the influence of gravity and strike the support structure in the pit of the dock leveler. This condition is known in the industry as free fall. Free fall can have unpleasant consequences, particularly when dock workers or material handling vehicles such as fork lifts are on the dock leveler during a time when free fall occurs. Some dock levelers are equipped with devices intended to mitigate the effects of free fall.
One such device used to limit the effects of free fall is a support structure known as a support leg. Typically, a dock levelers have a pair of support legs. After vehicles back up to a loading dock, the dock leveler typically is raised and the lip extended. The dock leveler is then lowered until the lip rests on the bed of the vehicle. When a dock leveler is engaged with a vehicle, the support legs may be slightly above a corresponding support structure configured to support the support legs. Thus, if free fall occurs, the support legs will only permit the dock leveler to fall a limited amount before the support legs engage the support structure.
One problem associated with support legs is that if a vehicle with a bed located below dock level backs up to the dock, the support legs may need to be retracted to allow the ramp to lower until the lip rests on the bed of the vehicle. If the support legs are not retracted, the deck will be supported at a level higher then the vehicle bed and the lip will fall to rest on the bed of the vehicle. Thus, the angle of the lip relative to the vehicle bed will be steeper than normal. This condition of the support legs preventing the ramp from being lowered is known in the industry as stump-out.
Stump-out can also occur as a vehicle is loaded. For example, the support legs may initially be above their support structure when the vehicle first backs up to a dock leveler. But as the vehicle is loaded and becomes heavier, the vehicle suspension may deflect due to the increasing load. As the vehicle bed becomes lower and lower the support legs may engage the support structure thus causing stump-out.
Stump-out can also occur when the support legs are still slightly above the corresponding support structure. As a fork truck moves in and out of the vehicle, deflection of the vehicle suspension will cause the vehicle and the dock leveler to move up and down several inches and cause the support legs to impact the corresponding support structure.
Stump-out can cause a variety of problems. For example, stump-out can lead to a lip angle, which may inhibit material handling equipment such as a fork lift from exiting the vehicle. The steep ramp may also cause the counterweight of a fork lift to impact the lip causing damage to the dock leveler. When stump-out is caused by deflection of the vehicle suspension, the repeated pounding of the support legs on the corresponding support structure can cause structural damage to the dock leveler and to the concrete pit that supports the dock leveler.
In order to avoid stump-out many dock levelers include retractable support legs. These legs can be retracted for servicing truck beds that are below dock level. Typically a pair of support legs are pivotally attached to the ramp near the lip hinge and extend downwardly to engage a supporting sub frame. These Support legs may be spring biased forward toward a supporting position and may be retracted to a non-supporting position by one of several means.
Both manual and automatic mechanisms have been used to retract support legs. Manual support leg retraction mechanisms may require an operator to engage a mechanism, for example, by pulling a chain to retract the support legs as the ramp is being lowered. Automatic support leg retraction mechanisms typically retract the support legs as the lip of the dock leveler is extended. In this way, the support legs are retracted when the lip engages a truck. However, retracting the support legs with manual mechanisms may require additional labor when trying to mate the dock lever to the truck, and retracting the support legs with automatic mechanisms may add complexity to the dock leveler.
Accordingly, a dock leveler that is able to deal with the problems of free fall and stump-out while at the same time reducing the amount of labor and complexity of a dock leveler is desired.
The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments includes a dock leveler that is able to deal with the problems of free fall and stump-out while at the same time reducing the amount of labor and complexity of a dock leveler.
In accordance with one embodiment of the present invention, a support leg system for a dock leveler is provided. The support leg system includes: a striker, a movable slider bar biased to a first position and configured to move from the first position to a second position when the striker engages the slider bar faster than a predetermined speed, and a first support leg operatively connected to the striker and configured to selectively move between a support position supporting a ramp portion of the dock leveler and a retracted position, the first support leg being biased to the support position and further configured to move to a retracted position when the striker engages the slider bar slower than a predetermined speed and stay in the support position when the striker engages the slider bar faster than the predetermined speed such that the slider bar moves to the second position.
In accordance with another embodiment of the present invention, a support leg system for a dock leveler is provided. The system includes: means for striking, means for sliding biased to a first position and configured to move from the first position to a second position when the striking means engages the sliding means faster than a predetermined speed. The system also includes, means for supporting a ramp portion of the dock leveler operatively connected to the striking means and configured to selectively move between a support position and a retracted position, the supporting means further configured to move to a retracted position when the striking means engages the sliding means slower than a predetermined speed and stay in the support position when the striking means engages the sliding means faster than the predetermined speed such that the sliding means moves to the second position.
In accordance with yet another embodiment of the present invention, a method of supporting a ramp portion of a dock leveler is provided. The method includes: at least one of: lowering a dock ramp faster than a predetermined speed and thereby cause a striker to deflect a slider bar and thereby cause a support leg to be in a support position; and lowering a dock ramp slower than a predetermined speed and thereby cause a striker to slide across a slider bar and thereby cause a support leg to retract.
There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.